Bug in quicksort example (K&R C book)?

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有刺的猬
有刺的猬 2021-02-15 12:50

This quicksort is supposed to sort \"v[left]...v[right] into increasing order\"; copied (without comments) from The C Programming Language by K&R (Second Edition):



        
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  • 2021-02-15 13:32

    You aren't imagining an array with INT_MAX number of elements, are you?

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  • 2021-02-15 13:33

    Yes, you're right, although it's possibly just written that way for simplicity -- it's an example after all, not production code.

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  • 2021-02-15 13:37

    Yes, you're right. You can use left - (left - right) / 2 to avoid overflows.

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  • 2021-02-15 13:43

    K&R was always a bit sloppy with their use of unsigned vs signed arguments. Side effect of working with a PDP that had only 16 kilobytes of memory I suppose. That's been fixed a while ago. The current definition of qsort is

    void qsort(
       void *base,
       size_t num,
       size_t width,
       int (__cdecl *compare )(const void *, const void *) 
    );
    

    Note the use of size_t instead of int. And of course void* base since you don't know what kind of type you are sorting.

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